1. Field of the Invention
This invention relates to a process for upgrading residual hydrocarbon oils to more valuable products, and more particularly to a process wherein hydrogen deficient residual petroleum oils are thermally cracked in the presence of a hydrogen donor diluent.
2. Description of the Prior Art
It is known in the art to upgrade hydrogen deficient residual petroleum oils (resid) by thermally cracking the resid in admixture with a hydrogen donor diluent. The hydrogen donor diluent is a material, generally aromatic-napthenic in nature, that has the ability to take up hydrogen under mild hydrogenation conditions and to readily release the hydrogen to a hydrogen deficient resid under thermal cracking conditions. One of the principal advantages of the hydrogen donor diluent cracking (HDDC) process is that it can upgrade resids which are not readily amenable to other conversion processes, and another principal advantage is that it can provide high conversions in the absence of a catalyst and with a minimum of coke deposition. The cracked materials produced by the HDDC process are readily recovered as desirable products including light ends and a gasoline fraction, and the hydrogen donor diluent can be recovered by fractionation of the cracked products and recycled through the hydrogenation step for reuse as donor diluent in the cracking unit.
The HDD process is well known in the art, and a comprehensive description of the process, including materials, flows, and operating conditions, appears in U.S. Pat. No. 2,953,513. Variations of the HDDC process, particularly as to the make-up of the hydrogen donor diluent, are described in U.S. Pat. Nos. 2,873,245 and 3,238,118. Hydrogen donors proposed in the prior art include relatively low boiling, pure, and expensive compounds such as naphthalene, tetralin, decalin, anthracene, and the like. These compounds have generally been considered unsatisfactory for a commercial operation because of their expense and other difficulties inherent in their use. More practical hydrogen donor diluents suggested by prior art include partially hydrogenated catalytic cycle oil, a partially hydrogenated lubricating oil extract or other partially hydrogenated aromatic. Hydrogen donors usually contain condensed ring aromatics in sufficient quantities to serve as a hydrogen carrier. These aromatics are partially hydrogenated; there is added to them some easily removable hydrogen atoms but not enough to convert the aromatics substantially to naphthenes.
U.S. Pat. No. 4,101,416 describes upgrading of tars derived from pyrolysis of coal by hydrogenation, and mentions that hydrogen donor solvents can play a role in this upgrading.
U.S. Pat. No. 4,090,947 describes a hydrogen donor diluent cracking process in which the donor is derived from a premium coking operation.